Generally, ascorbic acid acts as a reducing agent, a collagen synthesis promoter or an antioxidant, stimulates iron absorption in the small intestines, and is involved in carnitine biosynthesis and immunity. It is known that, when the body is deficient in ascorbic acid, scurvy, the abnormalities in connective tissue caused by abnormalities in collagen synthesis, bone pain, bone fracture, diarrhea, etc., may occur, and when an excessive amount of ascorbic acid exists in the body, gastrointestinal disorders, including nausea, abdominal pain, diarrhea and the like, may occur. In particular, the excellent antioxidant effect of ascorbic acid is known to inhibit melanin production in the skin, thereby preventing abnormal pigmentations such as freckles, and thus ascorbic acid is attracting attention as a material for skin external use.
Although ascorbic acid exhibits various effects as described above, it has problems in that it is mostly destroyed when being heated in air, is unstable against alkali, and is easily oxidized in an aqueous solution to lose such effects. Thus, in order to overcome this unstability of ascorbic acid, various ascorbic acid derivatives have been developed.
Previously developed ascorbic acid derivatives are as follows. First, there are derivatives such as phosphorylated ascorbic acid or metal salts thereof. Such derivatives are easily converted to an L-ascorbic acid form available in the human body, compared to other derivatives, but has a disadvantage in that they are difficult to absorb into the skin, because they have negative charges. Second, a variety of fatty acid-conjugated derivatives are known, including ascorbyl palmitate, ascorbyl laurate, ascorbyl stearate, etc. Among these derivatives, ascorbyl-6-palmitate is most widely used (see U.S. Pat. No. 5,409,693). These derivative compounds are absorbed into the skin, but have a disadvantage in that they are difficult to convert into an L-ascorbic acid form. Third, collagen-producing peptide-conjugated ascorbic acid derivatives are known in which a succinoyl group is linked to the hydroxyl group at carbon 5 or carbon 6 of ascorbic acid by an ester bond and the collagen-producing peptide is linked by an amide bond (see Korean Patent No. KR 10-0459679]. These derivatives show excellent efficacy compared to ascorbic acid, but have the disadvantage of having poor stability.
As described above, almost all ascorbic acid derivatives developed to date were not improved in terms of efficacy or stability compared to pure ascorbic acid, and peptide-conjugated ascorbic acid derivatives mostly have aimed to enhance only the whitening effect of ascorbic acid. Thus, the wide use of these derivatives for cosmetic applications is limited.